Screwing shiplap over shiplap

[Johnboy54]

Hi to all.
About 5 years ago I built a summerhouse.
4 x 2 timber frame. 4" insulation. 6 x 2 roof joists with 6" insulation. Floor insulated. Fire retardent plasterboards. Flush toilet. Electrics and alarm. Double glazed door and window.
I like to think I made a good job of it.
I did the walls with 18mm ply, battened and covered with breathable roofing felt.
I covered that with 12mm shiplap.
I treated it each year with Cuprinol wood preserver.
2 years ago, my wife thought she'd surprise me while I was away.
She coated it with some cheap water-based stuff.
It looks bad.
So bad I've bought new 18mm shiplap.

My question is, can I just screw the new on top of the old?

My thoughts are it would be OK, but I decided it's best to ask.
Getting all the frame sealant off will be a nightmare if I remove the old boards.
Forecast is mostly sun for the next 3 days so I'm hoping to get it done.

Thanks for any advice.

John

 

[sparkwright]

Seems like a lot of effort to hide a bad paintjob.

Was the Cuprinol wood preserver you used in the first place oil-based?

I'm assumed this cheap water-based stuff was put over an oil-based, almost shiny, surface - and hasn't soaked in well.

I'm wondering after two years if the cheap water based stuff would accept new preserver or similar now. I don't know if it's peeled, or would even scrub off.

As you have seen, the cheap water-based stuff that seems to be for sell everywhere doesn't always last long, and in some cases can even be seen deteriorating in the rain.

Cuprinol do a water-based preservative, which does soak in and last longer than the stuff I imagine your wife used.

Send a picture.

 

[Johnboy54]

Thanks for the reply.
As you can see it's many different shades.
She didn't take all the baskets off and stained around them.
Because I was so miffed last year, not knowing what to do with the mess, I didn't treat it.
This year, the panels have started shrinking and parting.
I did use oil based Cuprinol each year until the wife came along.
It's not a case of trying to save it now, as I've got new, thicker shiplap and the oil based Cuprinol.
It's just a question of going over it or removing it first.
Going over it is the easiest option, but I'm not sure how the old stuff would react over time, if at all.
And the good old weatherman has struck again!
Instead of the sunshine they promised we've got thick dark clouds.
Should be sacked.

Thanks sparkwright.

John

 

[big-all]

i use ducks back its quite waxy and it seals the surface not soaking in
i would say at around £12 for 5L so worth a go and build another shed with the timber

 

[sparkwright]

The 'ducks back' stuff is rubbish.

I think after two years you should remove all hanging baskets etc, and give the lot a good, even, sanding down - and treat with an oil-based stain.

Sikkens do a very good oil-based stain. It tends to stick very well. It is a two part system. The first part gives a matt finish, the second part is shinier. Just using the first part is fully acceptable, if you want a dull finish.

Or you could just carry on with the oil-based preserver you have already bought.

I can't see from your pictures anything too majorly wrong, but of course I'm not there looking at.

Is the water-based product flaking off, or has it adhered reasonably well?

Personally I think it's worth trying before you replace the wood.

Before we go into the technicalities of fitting new wood, I would say it's never a good idea to over-clad something. If any rot starts, or water finds a way in, you will have double trouble.

From a repair and replace point of view, it will be far simplier to only have one layer of wood, and I think you will regret over-boarding.

An electric sander will give you a good key to re-paint, though take it easy as if you sand too much in places you will end up with patchy spots, and you won't be happy.

 

[big-all]

well you are using different ducks back to me then
2 coats every 2 or three years 13 years on as good as new

 

[ironsidebod]

Likewise ducks back has been great on our fences. It went onto fresh wood though rather than old fence paint...

 

[sparkwright]

I have found the ducks back and similar products are ok on unweathered, treated wood, but to me it's not much use on weathered wood. It doesn't soak in enough.

When going over wood done in water-based ducks back, I tend to apply a more expensive water-based preserver over any bare wood, then for cheapness use ducks back over the lot.

Although I have had longer lasting results just using the water-based preserver, though can be double the price.

Sometimes water-based is preferable, less mess for a start.

This won't necessarily be the answer to the op's problem though, water-based over oil-based is not always a good idea, sometimes it works, depends exactly what products have been used.

 

[big-all]

yes i fully accept it may not work but will give a uniform finish with a couple off coats and if it lasts 24 months without peeling its got a good chance off keeping
if its going to fail would expect it to happen within 6 months or less

 

[Johnboy54]

Thanks for the many replies and excellent advice.
However, as I said in my original post, I've already bought the new timber (18mm this time from Homebase. Bargain.) and oil based Cuprinol.
I've gone with sparkwright's advice and removed the old cladding.
I'm glad I did because it makes the ends around edges a much neater job.
Thanks to all once again.
Regards
John